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Spin Networks : Physics

post #1 of 15
Thread Starter 
I know some members like this stuff. A new theory to replace strings. I saw this at /. and thought some here might like it.

<a href="http://www.sciam.com/article.cfm?articleID=0007E95C-9597-1DC9-AF71809EC588EEDF&catID=2" target="_blank">Throwing Einstein for a Loop</a>

Physicist Fotini Markopoulou Kalamara has developed a way to connect relativity with quantum theory--while making sure that cause still precedes effect.

By Amanda Gefter
post #2 of 15
I'd kill to be able to research this kind of stuff. As ever, though, thinking is way ahead of what we can physically prove.
Chicanery.
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Chicanery.
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post #3 of 15
That's pretty interesting stuff-I wonder how that is related to NCG.It dispenses with the point particle model as well.

Here is a link to one of her papers:

<a href="http://arxiv.org/abs/gr-qc/0203036" target="_blank">http://arxiv.org/abs/gr-qc/0203036</a>

[ 11-28-2002: Message edited by: Rick1138 ]</p>
post #4 of 15
Thread Starter 
she ****ing lost me at "spin foam". To me that's when your beer is turing around and around.
post #5 of 15
[quote]Originally posted by Scott:
<strong>she ****ing lost me at "spin foam". To me that's when your beer is turing around and around.</strong><hr></blockquote>
You aren't lost at all! That's exactly right. Well know fact: The universe revolves around alcohol. Or rather, scientists make it seem that way so that the can get away with putting large quantities of beer down on their expenses.
Chicanery.
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Chicanery.
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post #6 of 15
I thought the quantum 'limboness' theory was superseeded along time ago, by the feedback method? This doesn't need observers.? Have I gone wrong somewhere?
post #7 of 15
from the SciAm article:

But a spin network represents the entire universe, and that creates a big problem. According to the standard interpretation of quantum mechanics, things remain in a limbo of probability until an observer perceives them. But no lonely observer can find himself beyond the bounds of the universe staring back. How, then, can the universe exist? "That's a whole sticky thing," Markopoulou Kalamara says. "Who looks at the universe?" For her, the answer is: we do. The universe contains its own observers on the inside, represented as nodes in the network. Her idea is that to paint the big picture, you don't need one painter; many will do. Specifically, she realized that the same light cones she had used to bring causal structure into quantum spacetime could concretely define each observer's perspective.

If the universe needs an observer(s) inside it to keep it out of the limbo of probability and in reality then what kept it in reality before humans or other sentient beings spontaneously developed with-in the confines of this universe? This is a paradox that was not explained.

I understand the concept of light cones also; it's one of the reasons why we cannot travel faster than light in this universe. Imagine a person in a spaceship that can travel 4 times the speed of light. He is in orbit around a star 8 light years away. He has a missile that can destroy the star and he launches it to cause the collapse of the star. He then travels to earth at top speed (this takes him 2 years) and predicts the destruction of that star. If all goes well, in 6 years the star will explode in a fireshow that will be visable from earth because it take light 8 years to transverse the 8 light years minus the time it took him to get to earth. But lets say someone doesn't like the idea of this joker taking out a star for his own glory, so he hops in his Super Cruiser10 (that can travel 10 times the speed of light) and he gets there just before the first guy is about to destroy the star. So he blasts him to smithereens. So whats the problem? The problem is this second guy basically MADE his own light cone. They both did in fact. The first guy made a light cone by going to earth before earth's light cone showed the destruction of the star. he had knowledge that he should not have had; prediction of a future event. It's not like predicting weather either; it was a cosmilogical change induced by his actions. The second guy compounded it by nullifying the first light cone and introducing a new cone. But the star WAS destroyed. But because he interveened that effect was nullified in the universe. Just imagine the implications, just by travelling faster than light you force the immediate vicinity of that part of the universe to go BACK in time while the rest of the universe continues on it's own timeline! This would require infinate energy to acomplish. That's why faster than light travel is impossible and light cones cannot be tampered with.
post #8 of 15
I actually prefer my reason for not being able to travel faster than light.

Because when you reach the speed of light, the universe will instantly reach its end (as in time) OR because when you reach the speed of light, you will instantly crash into whatever it is you are heading towards. Providing the universe doesn't end first, um there can be no first. So you crash and the universe ends at the same time.

DO I NEED TO EXPLAIN ;-) !!!!
post #9 of 15
[quote]Originally posted by MarcUK:
<strong>I actually prefer my reason for not being able to travel faster than light.

Because when you reach the speed of light, the universe will instantly reach its end (as in time) OR because when you reach the speed of light, you will instantly crash into whatever it is you are heading towards. Providing the universe doesn't end first, um there can be no first. So you crash and the universe ends at the same time.

DO I NEED TO EXPLAIN ;-) !!!!</strong><hr></blockquote>

Actually, as you travel faster and faster your mass gets larger and larger. As you reach the speed of light your mass become infinite; you become a super mega black hole that sucks the whole universe into yourself. After you collapse onto yourself too.
post #10 of 15
If traveling at the speed of light causes mass to become so heavy....

Why then aren't we all sitting in the dark? :cool:
The Bush public works project to repave the road from Suspicion to Paranoia is over budget.
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The Bush public works project to repave the road from Suspicion to Paranoia is over budget.
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post #11 of 15
[ 11-30-2002: Message edited by: MarcUK ]</p>
post #12 of 15
OK I'll correct a few things. As something travels faster and faster in a certain referential, its INERTIAL mass as measured in this same referential is getting bigger. But is GRAVITATIONAL mass doesn't change. Those are 2 very distinct concepts. It just happens that when at rest, inertial and gravitational masses are EXACTLY equal. Therefore nothing about becoming a black hole or such happens.

And I'm not sure about this explanation that lights cones were there before, and the limiting speed of light is a consequence of the cones. It's the other way around. No information/matter/energy can travel faster than light, so there is a distance beyond which we can't have any contact or physical interactions. Light cones are not physical entities by themselves.

More on topic: like someone said, the "need" for an obersver in quantum mechanics was settled some time ago. "Observation" in the human sense is not what is meant. Observation is in fact a wrong choice of word but was kept since it was use at the beginning of quantum theory. It should be replaced by interaction. The quantum waves, the probabilistic superposition, collapse when they interfere with a macroscopic entity. And in a condensed bunch of atoms it happens quite frequently as you can guess, so matter is pretty much in a stable state.

Even more on topic: I read the article, and I didn't get much of what they were doing. They tried to only tell the general idea through a geometrical reprensantation, and ended up saying nothing. I'll try to find more details and understand what it really is about. Until then it's just another mathematical model.
post #13 of 15
I'm glad, Matlock is on the case!
post #14 of 15
[quote]Originally posted by Outsider:
<strong>I'm glad, Matlock is on the case! </strong><hr></blockquote>

Justice will prevail, don't worry.
post #15 of 15
[quote]Originally posted by Outsider:
<strong>I understand the concept of light cones also; it's one of the reasons why we cannot travel faster than light in this universe. Imagine a person in a spaceship that can travel 4 times the speed of light. He is in orbit around a star 8 light years away. He has a missile that can destroy the star and he launches it to cause the collapse of the star. He then travels to earth at top speed (this takes him 2 years) and predicts the destruction of that star. If all goes well, in 6 years the star will explode in a fireshow that will be visable from earth because it take light 8 years to transverse the 8 light years minus the time it took him to get to earth. But lets say someone doesn't like the idea of this joker taking out a star for his own glory, so he hops in his Super Cruiser10 (that can travel 10 times the speed of light) and he gets there just before the first guy is about to destroy the star. So he blasts him to smithereens. So whats the problem? The problem is this second guy basically MADE his own light cone. They both did in fact. The first guy made a light cone by going to earth before earth's light cone showed the destruction of the star. he had knowledge that he should not have had; prediction of a future event. It's not like predicting weather either; it was a cosmilogical change induced by his actions. The second guy compounded it by nullifying the first light cone and introducing a new cone. But the star WAS destroyed. But because he interveened that effect was nullified in the universe. Just imagine the implications, just by travelling faster than light you force the immediate vicinity of that part of the universe to go BACK in time while the rest of the universe continues on it's own timeline! This would require infinate energy to acomplish. That's why faster than light travel is impossible and light cones cannot be tampered with.</strong><hr></blockquote>

To me, this isn't making a damn bit of sense. Okay, SpaceMan1 decides to go to Star1, blows it to hell, travels 8 lightyears back to Earth at 8x lightspeed in two years, predicts the explosion of Star1, six years later, it happens. Gotcha.

But SpaceMan2, when does he leave, when SpaceMan1 comes to earth and predicts it, 1/10 of a year before SpaceMan1 decides to blow up the star, or when the light of the star blowing up reaches Earth?

If it was the latter, and SpaceMan2 travels to Star1 at 10x lightspeed, logic tells me he will see the star 1/10 of a year after it was blown up by SpaceMan1. SpaceMan1 will have departed 6.1 years ago. On the other hand, SpaceMan2 will be looking at Earth and will see it eight years in the past.

So how is it that SpaceMan2 kills SpaceMan1 again?

Now, if he left at the time that SpaceMan1 predicted the explosion, logic tells me that he would intercept the light given off when the star exploded 5.4545 lightyears away from Earth, then start passing through the light image, which would appear at an accelerated rate, only to arrive at Star1 2.1 years after Star1 Exploded.

<img src="confused.gif" border="0">

[ 12-01-2002: Message edited by: Spart ]</p>
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